1. Field of the Invention
The present invention relates to a can and a lithium secondary battery using the same. More particularly, the present invention relates to a can and a lithium secondary battery using the same, where guide slots are formed in a bottom wall and a sidewall of the can of the lithium secondary battery so that the can be symmetrically bent about a longitudinal axis thereof when the lithium secondary battery is compressed in a direction orthogonal to the longitudinal axis, thus preventing a short circuit from occurring between electrode plates leading to improved safety of the lithium secondary battery.
In addition, the present invention relates to a can and a lithium secondary battery using the same, where embossing portions are formed in a bottom wall of the can of the lithium secondary battery while protruding toward an inner portion of the can, so that the bottom wall of the can is outwardly bent when the lithium secondary battery is compressed in a direction orthogonal to the longitudinal axis of the can, leading to improved safety of the lithium secondary battery.
2. Description of the Prior Art
Recently, portable wireless appliances, such as video cameras, portable phones and portable computers, have been fabricated to be light-weight and equipped with various functions. As a result, studies have been actively performed in relation to secondary batteries used as power sources for these portable wireless appliances. For instance, the secondary batteries include Ni—Cd batteries, Ni—MH batteries, Ni—Zn batteries and lithium secondary batteries. Among other things, the lithium secondary batteries are rechargeable batteries, which can be fabricated to have a compact size with high capacity. The lithium secondary batteries represent high operational voltage and high energy density per unit weight, allowing the lithium secondary batteries to be extensively used in the advanced electronic technology fields.
A lithium secondary battery can be obtained by accommodating an electrode assembly, that includes a positive electrode plate, a negative electrode plate and a separator, into a can together with an electrolyte, and then sealing an upper opening of the can using a cap assembly. In general, the can is made out of aluminum or an aluminum alloy through a deep drawing process. In addition, a lower surface of the can is substantially planarized.
The electrode assembly is formed by winding the positive electrode plate together with the negative electrode plate while interposing the separator therebetween. A positive electrode tap is coupled to the positive electrode plate and an end portion of the positive electrode tap protrudes upward from the electrode assembly. A negative electrode tap is coupled to the negative electrode plate and an end portion of the negative electrode tap also protrudes upward from the electrode assembly. The positive electrode tap is spaced apart from the negative electrode tap by a predetermined distance so that the positive electrode tap can be electrically insulated from the negative electrode tap. In general, the positive and negative electrode taps are made out of nickel.
The cap assembly includes a cap plate, an insulating plate, a terminal plate and an electrode terminal. The cap assembly fits within an insulating case and is assembled to the upper opening of the can, thus sealing the can. The cap plate is made out of a metal plate having a size and a shape corresponding to that of the upper opening of the can. The cap plate is located at the center of upper opening and is perforated by a first terminal hole which accommodates the electrode terminal. When the electrode terminal is inserted into the first terminal hole, a gasket tube is fitted around the electrode terminal in order to insulate the electrode terminal from the cap plate. The electrode terminal is connected to the negative electrode tap of the negative electrode plate or the positive electrode tap of the positive electrode plate so that the electrode terminal can serve as a negative electrode terminal or a positive electrode terminal. An electrolyte injection hole having a predetermined size is located at one side of the cap plate. After the cap assembly has been assembled to the upper opening of the can, the electrolyte is injected into the can through the electrolyte injection hole. Then, the electrolyte injection hole is sealed by a plug.
The insulating plate is made out of an insulating material identical to the material used for the gasket and is coupled with the lower surface of the cap plate. The insulating plate is perforated by a second terminal hole that is aligned to the first terminal hole of the cap plate and into which the electrode terminal is inserted. The insulating plate is formed on the lower surface of the cap plate and has a resting recess having a size and a shape corresponding to that of the terminal plate so that the terminal plate can be rested in the resting recess.
The terminal plate is made out of a Ni alloy and is coupled with the lower surface of the insulating plate. The terminal plate is perforated by a third terminal hole that is aligned to the first terminal hole of the cap plate and into which the electrode terminal is inserted. Since the electrode terminal inserted into the first terminal hole of the cap plate is insulated from the terminal plate by means of the gasket tube, the terminal plate can be electrically connected to the electrode terminal while being electrically insulated from the cap plate.
Meanwhile, the negative electrode tap coupled to the negative electrode plate is welded to one side of the terminal plate and the positive electrode tap coupled to the positive electrode plate is welded to other side of the cap plate. The negative and positive electrode taps are welded to the terminal plate and the cap plate through resistance welding or laser welding. Of these, the resistance welding is preferred.
Recently, as the energy density of the lithium secondary battery has increased, the lithium secondary battery has become smaller in size, causing the lithium secondary battery to becomes more vulnerable to damage from impact and compression. Accordingly, when the lithium secondary battery is subject to such impact and compression, the electrode assembly within the can becomes deformed, causing a short circuit to be generated between electrode terminals, leading to accidental ignition or explosion of the lithium secondary battery.
In particular, when the lithium secondary battery is deformed about a longitudinal axis by longitudinal compression force applied thereto during a longitudinal compression test, which is one of safety tests for the lithium secondary battery, the can is completely compressed without forming a predetermined regular shape. Thus, irregular pressure is locally applied to the electrode assembly within the can, so that short circuiting can occur between electrode plates of the electrode assembly, causing accidental ignition or explosion of the lithium secondary battery. Therefore, what is needed is an improved design for the can and for the lithium battery where the electrode assembly is less apt to be damaged by impact and compression.